All control subjects were nonsmokers and had normal findings on chest radiographs, normal airway reactivity, and normal pulmonary function test results. Moreover, they had experienced no current respiratory symptoms, were nonatopic, and had experienced no respiratory infections within the previous month. None were receiving any medications. The study protocol was approved by the ethics committee of the Korea University College of Medicine and written informed consent was obtained from all subjects. The methacholine challenge was performed using the following method. Acetyl methacholine chloride (Sigma; St. Louis, MO) was diluted with normal saline solution and divided into nine solutions ranging from 0.075 to 25 mg/mL. Each solution was inhaled five times through a nebulizer (DeVilbiss Pulmoaide Compressor/Nebulizer; SM Instruments; Doylestown, PA) and a dosimeter (Micro-Dosimeter; Sunrise Medical; Carlsbad, CA). FEV1 was measured after each inhalation, and the PC20 was subsequently calculated from a log response curve by linear interpolation. Allergy treatment itat on Positive airway hyperresponsiveness was defined as a PC20 value of < 8 mg/mL. allergy treatment Atopy was defined as a positive reaction to the allergy skin-prick test or a total serum IgE level of > 100 IU/mL. The allergy skin-prick tests were performed using a solution (Bencard; Brentford, England) of 55 common allergen extracts. The ratios of the wheal size compared with that induced by a histamine solution were measured with a skin test reaction gauge (Bencard) 15 min after skin pricking. A negative result of the test indicated that there was no reaction induced by the allergen but that there was a normal reaction to the controlled histamine solution. A score of 1 + was given to erythema, and a score of 2 + was given to a wheal size ratio of < 1. Ratios between 1 and 2 were given a score of 3 +, and ratios between 2 and 3 were given a 4 +. Scores > 2+ were designated as positive. Total serum IgE levels were measured with paper radioimmunosorbent test kits (Radim; Rome, Italy), and levels > 100 IU/mL were defined as positive.